Effects of spatial fluctuations in the extragalactic background light on hard gamma-ray spectra

Kudoda, Ayman M.; Faltenbacher, A.

doi:10.1093/mnras/stx279

Cited by 7 publications

(7 citation statements)

References 48 publications

(37 reference statements)

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“…For the homogeneous EBL background (beyond 50 Mpc) we use our previous EBL forward model KF17 (Kudoda & Faltenbacher 2017), considering only the contribution form main-sequence stars to the EBL stellar component. The EBL at z = z1 is derived by integrating the contributions from stars of all masses formed throughout the history of the universe from z = 10 to z = z1.…”

Section: The Homogeneous Ebl Backgroundmentioning

confidence: 99%

“…Backward evolution models begin with the observed present day luminosity functions for galaxy populations in the local Universe and extrapolate them to higher redshift (e.g., Malkan & Stecker 1998;Rowan-Robinson 2001;Stecker et al 2006). Forward evolution models start with early structure formation scenarios to predict the galactic evolution forward in time (e.g., Dwek et al 1998;Razzaque et al 2009;Finke et al 2010;Kudoda & Faltenbacher 2017). Cosmic chemical evolution models consider basic galaxy ingredients such as gas, metallicity and radiation content and follow their evolution in a large comoving volume element (e.g., Pei & Fall 1995;Pei et al 1999).…”

Section: Introductionmentioning

confidence: 99%

“…The grey lines show the total EBL intensity along the various γ-ray paths (961 cylinders) starting from z = 0 up to z = 0.5. The red dash-doted line is the pure analytic approach KF17 fromKudoda & Faltenbacher (2017), the red dashed line shows an example of the integrated total EBL intensity in one cylinder . The γ-ray opacity averaged over all γ-ray paths at different redshifts.…”

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confidence: 99%

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Detailed modelling of the EBL along VHE γ-ray paths

Kudoda

Faltenbacher

2018

Monthly Notices of the Royal Astronomical Society

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Interactions between the extragalactic background light (EBL) and very high energy γ rays (VHE; E > 10 GeV) from cosmological sources alter their γ-ray spectrum. The stronger absorption of harder γ rays causes a steepening of the observed γ-ray spectrum at the high energy tail which can be expressed by an increase of the power index. The effect provides a link between high energy astrophysics and the evolution of galaxies. In this work we develop a new hybrid EBL model by augmenting our previous analytic model with information from semi-analytic galaxy catalogues. The model allows us to study the γ-ray opacities of individual γ-ray paths through the (simulated) universe and evaluate the effect of local fluctuations in the EBL intensity along each path. We confirm an order of magnitude fluctuations in the local EBL (based on the cumulative light from model galaxy distributions within spheres of 50 h −1 Mpc). However, the effect of these fluctuations on the VHE γ-ray opacity is insignificant due to the overall very small contribution of the local EBL to the total EBL. We also investigate the effect which a galaxy crossing the line of sight of the γray source may have on the VHE spectrum. We find that galaxies with stellar masses of M > 10 11 M could have significant effect on the γ-ray absorption. It is unlikely that the observed variation in the spectral index is caused by the proximity of single galaxies to the γ-ray paths as these are extremely rare.

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Section: The Homogeneous Ebl Backgroundmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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confidence: 99%

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Detailed modelling of the EBL along VHE γ-ray paths

Kudoda

Faltenbacher

2018

Monthly Notices of the Royal Astronomical Society

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“…Observation of the blazars by the large area telescope (LAT) onboard the Fermi satellite in energy range from 30 MeV to more than 500 GeV provides a very strong observational evidence regarding the intrinsic MeV-GeV emission from them [29]. Combined MeV-GeV and TeV observations have provided a new tool to constrain the EBL intensity [30,31,32,33,34,35,36,37]. Recently, the Fermi-LAT observations have been used to indirectly measure the EBL from the absorption features seen in the γ-ray spectra of blazars beyond the redshift z > 1 [38,39].…”

Section: Introductionmentioning

confidence: 99%

Extragalactic background light models and GeV-TeV observation of blazars

Singh

Meintjes

2020

NRIAG Journal of Astronomy and Geophysics

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The extragalactic background light (EBL) in the ultraviolet to far-infrared wavelength range is dominated by the emissions from stars in galaxies and reflects the time-integrated history of the light production and reprocessing in the Universe. Direct measurements of the EBL are affected by the interplanetary dust and galactic emission. Hence, the absolute level of EBL is subject to considerable uncertainties. Observations of very high energy (VHE) blazars located at cosmological distances by the Fermi-Large Area Telescope (LAT) and ground-based gamma-ray telescopes (e.g. H.E.S.S., MAGIC, VERITAS, TACTIC) provide a measurement of the EBL that is independent of the direct observations. The interaction of VHE or TeV photons originated from the distant blazars with the low energy EBL photons via e − e + pair-production can be used as a powerful tool to probe the different EBL models in the wavelength range 0.1-1000µm. In this paper, we use two different methods to determine the opacity of the VHE γ-ray photons caused by the low energy EBL photons and study the consequences of six different EBL models. The first method-Model-Dependent Approach, uses various EBL models for estimating the opacity as a function of the source redshift and energy. The second method-Model-Independent Approach, relies on using the simultaneous observations of blazars in the MeV-GeV energy range from the Fermi-LAT and in TeV band from the ground-based Cherenkov telescopes. We make underline assumption that the extrapolation of the LAT spectrum of blazars to TeV energies is either a good estimate or an upper limit for the intrinsic VHE spectrum of the source. We apply this method on the simultaneous observations of a few blazars PKS 2155-304, RGB J0710+591, 1ES 1218+304 and RBS 0413 at different redshifts to demonstrate a comparative study of six prominent EBL models. Opacities of the VHE γ-ray photons predicted by the Model-Independent Approach are systematically larger than the ones estimated from the Model-Dependent Approach using the six EBL models. Therefore, the γ-ray observations of blazars can be used to set a strict upper limit on the opacity of the Universe to the VHE γ-rays at a given redshift.

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“…While the statistical significance of these two indications is still modest due to a limited sample used in F15 (∼2.5σ ), these effects are in line with other deviations from the absorption-only model that neglects secondary emission from electron-positron pairs produced by primary very high energy (VHE, E >100 GeV) γ-rays. It was shown that EBL fluctuations are not strong enough to account for such an effect (F15, [12]- [13]). In this paper we present an astrophysical interpretation of the effects considered by F15 in the framework of the intergalactic electromagnetic cascade model [14] (hereafter D17).…”

Section: Introductionmentioning

confidence: 99%

An excess of extreme TeV blazars from the Fermi LAT distribution on the voidiness parameter

Khalikov¹,

Dzhatdoev²

2017

Proceedings of 35th International Cosmic Ray Conference — PoS(ICRC2017)

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Recently it was found that Fermi LAT blazars with relatively hard (γ <3) observed spectra above 10 GeV are predominantly located towards the directions to voids in the large scale structure and, moreover, the observed flux of E >10 GeV γ-rays is usually greater for the case of such directions. This effect may be interpreted in the framework of the "electromagnetic cascade model" (T.A. Dzhatdoev et al., A&A, 603, A59 (2017)). Namely, the secondary (cascade) component significantly enhances the observable flux in the 10-500 GeV energy region, rendering the sources brighter in this energy range. The model predicts the existence of a new population of blazars with very hard spectra in the 10 GeV-1 TeV energy region that could be discovered in future by the CTA observatory.

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Effects of spatial fluctuations in the extragalactic background light on hard gamma-ray spectra

Cited by 7 publications

References 48 publications

Detailed modelling of the EBL along VHE γ-ray paths

Detailed modelling of the EBL along VHE γ-ray paths

Extragalactic background light models and GeV-TeV observation of blazars

An excess of extreme TeV blazars from the Fermi LAT distribution on the voidiness parameter

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